• Transactions of the Korean Society of Automotive Engineers
• /
• v.14 no.6
• /
• pp.151-159
• /
• 2006

A one-dimensional numerical analysis is carried out to investigate the effects of inlet gas humidities, inlet gas pressures, and thicknesses of membrane on the performance of a proton exchange membrane fuel cell. It is found that the relative humidity of inlet gases at anode and cathode sides has a significant effect on the fuel cell performance. Especially, the desirable fuel cell performance occurs at low relative humidity of the cathode side and at high humidity of the anode side. In addition, an increase in the pressure ranging from 1 atm to 4 atm at the cathode side results in a significant improvement in the fuel cell performance due to the convection effect by a pressure gradient toward the anode side, and with decreasing the thickness of membrane, the fuel cell performance is enhanced reasonably.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.19 no.3
• /
• pp.116-124
• /
• 2009

Our computational studies for the physical vapor transport crystal growth of $Hg_2Cl_2-Cl_2$ system evidence suggests that the PVT growth process exhibits the diffusion-dominated behaviors for aspect ratios more than and equal to 10, which would provide purely diffusive transport conditions adequate to microgravity environments less than $10^{-3}g_0$. Also, the regimes of high temperature difference based on the fixed source temperature of $380^{\circ}C$, where ${\Delta}T$ is relatively large enough for the crystal growth of mercurous chloride, the transport rates do not keep increasing with ${\Delta}T$ but tend to some constant value of $2.12\;mole\;cm^{-2}s^{-1}$. For the aspect ratios of 5, 10, and 20, the transport rate is directly proportional to the total pressure of the system under consideration. For Ar = 5, the rate is increased by a factor of 2.3 with increasing the total pressure from 403 Torr to 935 Torr, i.e., by a factor of 2.3. For both Ar = 10 and 20, the rate is increased by a factor of 1.25 with increasing the total pressure from 403 Torr to 935 Torr.

• Journal of Environmental Science International
• /
• v.13 no.7
• /
• pp.655-660
• /
• 2004

This paper demonstrates the numerical simulation of three dimensional flow pattern for vehicular exhaust dispersion in the street canyons. The wind flow around buildings in urban is computed by the SIMPLEST method. The convection-diffusion equation was used to compute the $NO_X$ concentration level near buildings. Details are given of important boundary conditions and turbulence quantities variations. The simple turbulence model was used for unisotropic viscous effect. A control-volume based finite-difference method with the upwind scheme is employed for discretization equation. The simple turbulence model applied in this study has been verified through comparison between predicted and measured data near buildings. By the predictive results, the updraft induced by the presence of high-rise buildings is important in the transport of street level pollutant out from the street canyons. Our suggestion for reducing ground level pollution is to have high-rise buildings constructed or to reduce the channelling effect of street canyons.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.10 no.5
• /
• pp.955-961
• /
• 2009

Present, a portable battery have problem that the volume increases according to capacity Increase. Direct Methanol Fuel Cell is alternative by solution plan of this problem. In this paper, the characteristics of DMFC are analyzed by change in concentration and discharge of fuel in natural convection and room temperature condition. According to the analysis result, polarization by delay of diffusion velocity of hydrogen ion appeared in methanol of low concentration. And if have a lot of supplies of methanol, generation power declines by electric cell cooling effect.

• Journal of the Korean Vacuum Society
• /
• v.9 no.2
• /
• pp.172-178
• /
• 2000

We developed the model equations to investigate the particle movement and growth theoretically in a-Si plasma CVD reactor, where those particles act as the source of contamination. We included the effects of fluid convection, particle diffusion and external forces (ion drag force, electrostatic force and gravitational force) onto the particles to analyze the movements of particles in plasma reactor. Taking into account the particle charge distribution, the particle growth by coagulation between the charged particles was investigated. Most of those particles are located in the region near the sheath boundaries by the balance between the ion drag and electrostatic forces. The particle concentrations in the sheath region and in the bulk plasma region are almost zero. The sizes of the predator particles increase with time by the coagulation with protoparticles and, as a result, the surface area and the average charge of predator particles also increase with time.

• Particle and aerosol research
• /
• v.5 no.1
• /
• pp.17-27
• /
• 2009

Particle deposition on a semiconductor wafer larger than 100 mm was studied experimentally and numerically. Particularly the electrostatic effect on particle deposition velocity was investigated. The experimental apparatus consisted of a particle generation system, a particle deposition chamber and a wafer surface scanner. Experimental data of particle deposition velocity were obtained for a semiconductor wafer of 200 mm diameter with the applied voltage of 5,000 V and PSL particles of the sizes between 83 and 495 nm. The experimental data of particle deposition velocity were compared with the present numerical results and the existing experimental data for a 100 mm wafer by Ye et al. (1991) and Opiolka et al. (1994). The present numerical method took into consideration the particle transport mechanisms of convection, Brownian diffusion, gravitational settling and electrostatic attraction in an Eulerian frame of reference. Based on the comparison of the present experimental and numerical results with the existing experimental results the present experimental method for a 200 mm semiconductor wafer was found to be able to present reasonable data.

• Journal of computational fluids engineering
• /
• v.2 no.2
• /
• pp.59-72
• /
• 1997

A numerical model is constructed to simulate the interactions of oblique shock wave / turbulent boundary layer on a strongly heated wall. The heated wall temperature is two times higher than the adiabatic wall temperature and the shock wave is strong enough to induce boundary layer separation. The numerical diffusion in the finite volume method is reduced by the use of a higher order convection scheme(UMIST scheme) which is a TVD version of QUICK scheme. The turbulence model is Chen-Kim two time scale model. The comparison of the wall pressure distribution with the experimental data ensures the validity of this numerical model. The effect of strong wall heating enlarges the separation region upstream and downstream. In order to eliminate the separation, wall suction is applied at the shock foot position. The bleeding slot width is about same as the upstream boundary layer thickness and suction mass flow is 10% of the flow rate in the upstream boundary layer. The final configuration of the shock reflection pattern and the wall pressure distribution approach to the non-viscous value when wall suction is applied.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.14 no.5
• /
• pp.424-432
• /
• 2002

Numerical analysis has been conducted to characterize deposition rates of aerosol particles onto a heated, rotating disk with electrostatic effect under the laminar flow field. The particle transport mechanisms considered were convection, Brownian diffusion, gravitational settling, thermophoresis and electrophoresis. The aerosol particles were assumed to have a Boltzmann charge distribution. The electric potential distribution needed to calculate local electric fields around the disk was calculated from the Laplace equation. The Coulomb, the image, the dielectrophoretic and the dipole-dipole forces acting on a charged particle near the conducting rotating disk were included in the analysis. The averaged particle deposition vetocities and their radial distributions on the upper surface of the disk were calculated from the particle concentration equation in a Eulerian frame of reference, along with a rotation speed of 0∼1,000rpm, a temperature difference of 0∼5K and a charged disk voltage of 0∼1000V.Finally, an approximate deposition velocity model for the rotating disk was suggested. The present numerical results showed relatively good agreement with the results of the present approximate model and the available experimental data.

• Journal of applied mathematics & informatics
• /
• v.35 no.3_4
• /
• pp.241-260
• /
• 2017

An analysis is made to study the solute transport in a Casson fluid flow through an annulus in presence of oscillatory flow field and determine how this flow influence the solute dispersion along the annular region. Axial dispersion coefficient and the mean concentration expressions are calculated using the generalized dispersion model. Dispersion coefficient in oscillatory flow is found to be a function of frequency parameter, Schmidt number, and the pressure fluctuation component besides its dependency on yield stress of the fluid, annular gap and time in the case of steady flow. Due to the oscillatory nature of the flow, the dispersion coefficient changes cyclically and the amplitude and magnitude of the dispersion increases initially with time and reaches a non - transient state after a certain critical time. This critical value varies with frequency parameter and independent of the other parameters. It is found that the presence of inner cylinder and increase in the size of the inner cylinder inhibits the dispersion process. This model may be used in understanding the dispersion phenomenon in cardiovascular flows and in particular in catheterized arteries.

• Korea-Australia Rheology Journal
• /
• v.17 no.2
• /
• pp.47-62
• /
• 2005

The present study deals with a mathematical model describing the dynamic response of heat and mass transfer in blood flow through bifurcated arteries under stenotic condition. The geometry of the bifurcated arterial segment possessing constrictions in both the parent and the daughter arterial lumen frequently appearing in the diseased arteries causing malfunction of the cardiovascular system, is formulated mathematically with the introduction of the suitable curvatures at the lateral junction and the flow divider. The blood flowing through the artery is treated to be Newtonian. The nonlinear unsteady flow phenomena is governed by the Navier-Stokes equations while those of heat and mass transfer are controlled by the heat conduction and the convection-diffusion equations respectively. All these equations together with the appropriate boundary conditions describing the present biomechanical problem following the radial coordinate transformation are solved numerically by adopting finite difference technique. The respective profiles of the flow field, the temperature and the concentration and their distributions as well are obtained. The influences of the stenosis, the arterial wall motion and the unsteady behaviour of the system in terms of the heat and mass transfer on the blood stream in the entire arterial segment are high­lighted through several plots presented at the end of the paper in order to illustrate the applicability of the present model under study.